JPS6144611B2 - - Google Patents

Description

Claim 1: A voltage application and control device that applies a unidirectional voltage between an electrode and a workpiece to generate a spark discharge in a gap between the electrode and the workpiece during machining;
an EDM device that generates a monitor signal indicative of a change in arc discharge from a spark discharge in the gap; applying said unidirectional voltage to the gap without interruption until the gap indicates a low condition and maintaining this voltage, and then discontinuing the application of said voltage to the gap for a time to allow ionization in the gap to dissipate; 1. An EDM device comprising: in its operation repeatedly applying the voltage to the gap and removing the voltage from the gap in response to instructions from a monitor signal.

2. In claim 1, the voltage application and control device is configured to apply the voltage to the gap until the onset of arcing, when the monitor signal indicates that there is no spark discharge in the gap, and the time period is at least sufficient for deionization within the gap.
EDM equipment.

3. In claim 1 or 2, the monitor device comprises an antenna arranged to receive electromagnetic radiation generated from the gap, and a device that outputs a monitor signal from the signal received by the antenna. EDM equipment with.

4. According to claim 1 or 2, the monitoring device comprises an electrical connection to the electrode and/or the workpiece, and a device for outputting a monitoring signal from a signal received via the electrical connection.
EDM equipment.

5. The EDM according to claim 1 or 2, wherein the voltage application and control device has a DC power supply connected to the gap via a switching device in operation.
The apparatus includes a voltage application and control device comprising: a comparator that generates a first control signal when the monitor signal is at or above a predetermined level; a pulse generator for generating a second control signal after a predetermined time period equal to said time; The present invention is characterized by having an OR gate device that continuously conducts the switching device when a control signal is present and renders the switching device non-conductive when neither the first control signal nor the second control signal is present. EDM equipment.

6. The EDM according to claim 1 or 2, wherein the voltage application and control device has a DC power source connected to the gap via a switching device in operation, and conduction by the switching device is controlled in accordance with a monitor signal. 1. An EDM device comprising a device for superimposing an oscillating voltage whose amplitude is smaller than the magnitude of the voltage applied to the gap by a DC power source onto the voltage applied to the gap.

7. The EDM device according to claim 6, in which the repetition frequency of the oscillating voltage is in the range of 50 to 100 KHz.

8 Applying a unidirectional voltage between the electrode and the workpiece to generate a spark discharge in the gap between the electrode and the workpiece during machining, showing a change from spark discharge in the gap to arc discharge. A method of electrical discharge machining comprising obtaining a monitor signal, applying said unidirectional voltage to the gap without interruption until the monitor signal indicates a low degree of spark discharge associated with initiation of arc discharge, the application of said voltage to the gap being maintained for a period of time and thereafter discontinuing the application of said voltage to the gap for a time to allow ionization within the gap to dissipate, said voltage being repeatedly applied to and removed from the gap as directed by a monitor signal from the gap; An electric discharge machining method characterized by:

9. In claim 8, the voltage is applied to the gap until the onset of arcing, when the monitor signal indicates that there is no spark discharge in the gap;
The electrical discharge machining method is such that the time is at least sufficient for deionization within the gap.

Description The present invention relates to a method and apparatus for electrical discharge machining (EDM), also known as spark erosion machining.

In prior art EDM processing, once a spark discharge occurs in the gap between the electrode of the EDM equipment and the workpiece, the voltage applied to the gap is removed for a sufficient period of time to cause the ions in the gap to dissipate, for example. This is based on the fact that spark discharge will inevitably degenerate into arc discharge unless the discharge is interrupted. That is, the voltage is typically applied as a series of pulses of predetermined duration. That is, the pulse continues until the integrated gap current reaches a predetermined value.

Therefore, the time required for the electrical discharge machining operation is:
This is considerably longer than theoretically required.

An object of the present invention is to shorten the time required to perform EDM processing operations.

According to a first aspect of the present invention, a voltage application and control method applies a unidirectional voltage between an electrode and a workpiece to generate a spark discharge in a gap between the electrode and the workpiece during machining. an EDM device, the voltage application and control device comprising: an EDM device that generates a monitor signal indicative of a change in arc discharge from a spark discharge in the gap; Applying said unidirectional voltage to the gap without interruption and maintaining this voltage until a low degree of discharge is indicated, and then discontinuing the application of said voltage to the gap for a period of time to allow the ionization within the gap to dissipate. The EDM is configured to repeatedly apply the voltage to the gap and remove the voltage from the gap in response to instructions from a monitor signal in its operation.
Equipment provided.

According to a second aspect of the invention, a unidirectional voltage is applied between the electrode and the workpiece to create a spark discharge in the gap between the electrode and the workpiece during machining, and A method of electrical discharge machining comprising obtaining a monitor signal indicative of a change from a spark discharge to an arc discharge, the method comprising: obtaining a monitor signal indicative of a change from a spark discharge to an arc discharge; A directional voltage is applied to the gap and maintained between the gaps, and then the application of said voltage to the gap is interrupted for a time to allow ionization within the gap to dissipate, and said voltage is increased as indicated by a monitor signal from the gap. A method of electrical discharge machining is provided which is characterized in that a gap is repeatedly applied and removed.

The inventors of the present invention have discovered, through photographic observation of electrical discharge during machining, that during good machining, the electrical discharge between the electrode and the workpiece during voltage pulse application is a plurality of individual sparks. It was found that the machining is degraded when the voltage pulse includes an arc discharge period. Previously, each pulse was thought to begin as a spark that turned into an arc. According to the findings of the inventors, a voltage may be continuously applied between the electrode and the workpiece, and the voltage may be interrupted according to an indication of the occurrence of arc discharge by a monitor.

Monitoring of the discharge in the gap can be carried out, for example, by optical or electromagnetic radiation (including induced and radiated fields) or by electrostatic or magnetic fields associated with the voltage applied to the gap or the current in the gap. This is done by detecting the energy emitted from the gap. Of course, the signals generated by these methods of detection are required to distinguish between arc discharges and spark discharges. When detecting electromagnetic radiation, an antenna placed near the gap may be used, in which case signals in the frequency range of at least 16 to 24 MHz and 26 to 60 MHz should give a good discrimination between arc discharges and spark discharges. I understood. That is, the amplitude of those signals received is progressively larger during a spark discharge than during an arc discharge, and becomes smaller as the spark discharge approaches the arc discharge.

The difference in electromagnetic and optical radiation from the gap is thought to be due to two mechanisms. First, because a spark has a relatively short duration compared to an arc, the rate of change of current in the gap is greater during a spark discharge. Second
Additionally, when ionization occurs in arc discharges and spark discharges, the energy level of the electrons involved changes in different ways. In an arc discharge, where a relatively large amount of energy is supplied, larger energy level changes occur more often, recombination occurs less frequently, and the electrons assume intermediate states more often than in a spark discharge. If there are many changes in energy level, such as in a spark discharge where a small amount of energy is supplied, electromagnetic radiation of greater intensity and higher frequency is generated, and many electrons assume intermediate energy levels, as in an arc discharge. In this case, a lot of light of different frequencies is generated.

Furthermore, during an arc discharge light is generated substantially continuously, whereas during a spark discharge the light generation is intermittent and corresponds to the spark. The intermittency of light emission during the spark discharge can thus be exploited for the generation of a monitor signal.

Another way to monitor electrical discharges in the gap is to connect directly or indirectly to the electrodes and/or the workpiece a circuit for detecting the voltage applied to the gap or the radio frequency signal contained in the current in the gap. You may. The amplitude of the signal in the range 5 to 10 MHz and 25 to 30 MHz is
They are gradually larger during a spark discharge than during a spark discharge, and these amplitudes also become smaller as the spark discharge approaches an arc discharge.

Other methods can be used to distinguish between spark discharge and arc discharge, such as monitoring the voltage applied to the gap. This is because when a spark discharge turns into an arc discharge, this voltage drops slightly.

Hereinafter, embodiments of the present invention will be described by way of example with reference to the accompanying drawings.

FIG. 1 is a block diagram of the electrical circuit of an EDM device according to the present invention.

FIG. 2 shows the waveforms that appear in the circuit of FIG.

In FIG. 1, the antenna 30 is placed near the gap 25 between the electrode 11 and the workpiece 10 of the EDM equipment, or around a tank containing a dielectric liquid in which the electrode and workpiece are immersed. The antenna is connected to a detector 41 via an amplifier 40. Detector 41 may simply include a series diode and a shunt capacitor. The amplifier 40 has an output signal amplitude that depends on an input signal amplitude, and preferably has a linear gain characteristic. This amplifier is frequency selective and approximately
Tuned to accept 30MHz signals.

The detector 41 is connected to one input of a comparison circuit 52 which also receives an adjustable level obtained from a potentiometer 53. The output of the comparator 52 is sent to the drive circuit 1 for one group of transistors 18 via an OR gate 71.
8', and this group of transistors supplies current and voltage from the DC power supply 17 to the gap 25 when in a conductive state. In Figure 1,
An optional square wave oscillator 19 is also shown, the function and operation of which will be discussed below.

The output of comparator 52 also via inverter 59 triggers pulse generator 70 which sends a pulse to OR gate 71 10 milliseconds after receiving the input from inverter 59 .

In operation, when machining is to be carried out, there is no spark in the gap and therefore there is virtually no 30 MHz radiation received by antenna 30. Therefore, the comparator output is zero and
After a 10 millisecond delay, pulse generator 70 is triggered to generate a pulse. This pulse is supplied to the drive circuit 18' via the OR gate 71 and turns the transistor group 18 on. Therefore, if conditions for a spark discharge are present, high level radio frequency radiation is initiated and the signal from comparator 52 remains a signal that causes transistor group 18 to continue conducting. The spark discharge in the gap continues until an arc occurs at time 73 in FIG. 2, which shows the output waveform of OR gate 71. At that time, there is no signal from the comparator and transistor group 18 immediately ceases conducting. The waveform in Figure 2 then drops to zero and 10
The millisecond time interval ensures that the arc's ionization channel dissipates. The beginning of this time interval is triggered by comparator 52 via inverter 59 and ends when pulse generator 70 provides a starting pulse to OR gate 71. This process continues as shown in FIG. Second
In the figure, the output level of OR gate 71 during spark discharge is indicated as "spark discharge." Furthermore, the arc that occurs at time 74 is also
Shown with subsequent cessation and resumption of spark discharge.

The advantage of the device of Figure 1 is that it clearly provides a very high machining efficiency, since the spark discharge is not interrupted until the arc occurs, and the interruption after the arc is long enough to dissipate the ionization channel. That's what you get. The waveforms shown in FIG. 2 are for illustrative purposes only; in reality, of course, spark discharge occurs during most of the machining time. Provision is made to clean the gap if short spark discharge cycles continue.

Rough machining and fine machining used at the beginning and end of a machining operation are often controlled by using long machining pulses to start the operation and short pulses at the end. In the device of FIG. 1, this adjustment is not possible since the drive is applied at all times when a spark discharge occurs. However, rough and fine machining can be achieved by adjusting the power supplied to the gap, for example by controlling the operation of some of the transistors in transistor group 18.

The device of FIG. 1 consists of an oscillator 1 with a square wave output.
9. This oscillator has the function of maintaining spark discharge conditions by superimposing an oscillating voltage in the frequency range of eg 50 to 100 KHz on the gap voltage. Since the oscillator 19 is connected in series with the transistor group 18, its output voltage will be applied to the gap only when the voltage of the power supply 17 is applied to the gap 25. In a typical system, the voltage applied to the gap by the DC power source is 85 volts and the amplitude of the superimposed voltage is 15 volts.

The apparatus of FIG. 1 further connects a DC power supply 17 and transistor groups 18 and 19 to an SCR bridge (not shown), between which the AC power supply is connected between two terminals and the electrode and the workpiece are connected to the opposite terminals. ) can be changed by replacing it with In this case, the four SCRs of the bridge are:
The output from gate 71 triggers directly through the drive circuit, but of course only those with the correct polarity due to the power supply at that moment are rendered conductive. It is also possible to replace these SCRs with SCSs, which has the advantage that as soon as an arc is detected, the conducting SCS is switched off and the arc is stopped. .

Although specific embodiments of the invention have been described above, the invention may be practiced in many other ways. For example, the circuit for distinguishing between spark discharge and arc discharge and the circuit for applying voltage to the gap may be different circuits.